The testability of an electrical appliance (embedded, domestic, etc.), i.e. the capacity of the electrical appliance to detect and locate a fault disturbing its operation, constitutes a major issue in designing said electrical appliance. Good testability, leading to high rates of detection and location being obtained, is advantageous at the time the electrical appliance is manufactured, since such high rates make it possible to guarantee that the electrical appliance as delivered to the user is operational. When the electrical appliance is in service with a user, good testability also makes it possible to diagnose a fault effectively and to guide the user quickly towards an appropriate solution for correcting the fault.
For an electrical appliance of the modem, residential gateway, television decoder, etc., type, e.g. having a communications interface of the asymmetrical digital subscriber line (ADSL) type, in the event of there being a problem impacting the Internet access of the electrical appliance, it is appropriate to determine whether the problem comes from the ADSL communications interface of the electrical appliance or else from an element that is external to the appliance (Ethernet electric cable, ADSL filter, telephone socket, telephone line, etc.). A method that is presently in use for testing the communications interface consists in disconnecting the Ethernet electric cable, in connecting the electrical appliance to a test accessory delivered with the electrical appliance, and including a 100 ohm resistor simulating the impedance of the telephone line and of the electric cable, and in running a test program for testing the communications interface.
That method presents a certain number of drawbacks. At the time the electrical appliance is manufactured, it requires action on the part of a technician on the production line, which presents an impact that is not negligible in terms of duration and cost in manufacturing the electrical appliance. When the electrical appliance is in service with a user, that method requires the user to perform actions that are technically relatively complex for most users. That method also requires the use of the test accessory, and since it is used rarely there is a high risk of it being mislaid by the user. In the event of the test accessory being lost, the user is therefore obliged to take the electrical appliance to an agency or to a point-of-sale even though it is entirely possible that the electrical appliance is fully operational.